OBSERVATIONS OF THE HISTOLOGY OF STRIPED MUSCLE. 75 



These observations confirm Retzius' results^ viz. that the 

 transverse portions of the muscle network are directly con- 

 nected with the muscle-corpuscles; and, furthermore, that the 

 network is directly continuous with the intra-nuclear network 

 of the corpuscles. 



Development of the Network. 



This I have studied in embryos of the trout and rat. 



Trout. — In some gold preparations of embryo trout, taken 

 from the ova, I found developing muscle-fibres in an early 

 stage. These consisted of a portion of undifferentiated proto- 

 plasm containing the nucleus, and a portion already trans- 

 versely striated. Under a comparatively high power the 

 transversely striped portion showed darkly stained masses of 

 an ellipsoidal shape arranged side by side, and causing the 

 appearance of striation. Under a very high power {-^ immer- 

 sion) the network could be seen between these darkly stained 

 masses, and in the same form in which it appears in the adult 

 fibre. The dark masses appear to be some substance altered 

 by the method of staining, and shrunken in the meshes of the 

 network (figs. 7, 8 and 9). No connection was seen between 

 the network and the nucleus. 



In older fibres the network is more fully developed, but still 

 no connection appears to exist between the nuclei and the 

 network (fig. 10). 



Eat. — In developing muscle-fibre from the embryo rat the 

 fibres consist of an axial core of undifferentiated protoplasm 

 containing the nuclei, and a peripheral part with developing 

 network. Here, again, no connection was observed between 

 the nuclei and the network. 



It thus appears that — 



1. The network appears at a very early stage. 



2. It develops in its permanent form, and is not produced by 

 the transformation of an irregular network into the adult type. 



3. Each muscle-fibre is probably developed from a single 

 cell, and is not formed by a coalescence of cells, either end to 



